The present invention relates generally to a thermal radiation shield particularly suited for a Magnetic Resonance Imager (MRI) System and more particularly, to a method and apparatus for shielding radiation heat transfer between a radio frequency (RF) shield and a patient bore former.
Currently, Magnetic Resonance Imager (MRI) systems have included a superconducting magnet that generates a temporally constant primary magnetic field. The superconducting magnet is used in conjunction with a magnetic gradient coil assembly, which is sequentially pulsed, to create a sequence of controlled gradients in the static magnetic field during a MRI data gathering sequence. The controlled gradients are effectuated throughout a patient imaging volume (patient bore) which is coupled to at least one MRI (RF) coil or antennae. The RF coils are located between the magnetic gradient coil assembly and the patient bore.
As a part of a typical MRI, RF signals of suitable frequencies are transmitted into the patient bore. Nuclear magnetic resonance (nMR) responsive RF signals are received from the patient bore via the RF coils. Information encoded within the frequency and phase parameters of the received RF signals, by the use of a RF circuit, is processed to form visual images. These visual images correspond to the distribution of nMR nuclei within a cross-section or volume of the patient within the patient bore.
Current MRI systems require higher magnetic gradient coil assembly temperatures due to high power densities. Modern MRI systems also have decreased the amount of space between the magnetic gradient coil assembly and the outer surface of the patient bore, thereby, eliminating the potential for active cooling in the patient bore. Therefore, a passive cooling method is needed to reduce heat transfer from the magnetic gradient coil assembly to the RF coils and patient bore. A thermal radiation shield is a passive cooling method that has been used in other areas of industry, separate from MRI systems, to reduce heat transfer.
Thermal radiation shields with infrared properties are known, in the art, to greatly decrease the amount of heat transfer. In the past, thermal radiation shields have possessed infrared reflective properties due to their metalized coatings. The metalized coatings cause the shields to be electrically conductive.
If an electrically conductive shield were used between the RF coil and the magnetic gradient coil assembly it may degrade the resonant electrical properties of the RF circuit and possibly the fidelity of the nMR signal. An electrically conductive shield may also cause the production of detrimental eddy currents. As eddy currents produce their own magnetic fields, the magnetic fields produced by these eddy currents can cause interference with the MRI imaging process.
If an infrared reflective shield were used between the RF coil and the RF shield it may cause interference with the RF wavelengths of interest during MRI operation. The interference with the RF wavelengths of interest may cause MRI imaging problems.
In combination with the aforesaid, MRI systems that comprise a metallic outer surface of the patient bore may also have RF interference with the nMR signals caused by these metallic surfaces.
It would therefore be desirable to provide a method to reduce the heat transfer from the gradient coil to the patient bore and RF coils without degradation of nMR signals in current MRI systems.
It is therefore an object of the present invention is to reduce the amount of radiation heat transfer between an outer surface of a patient bore and an inner surface of a magnetic gradient coil assembly of a magnetic resonance imager (MRI) system and not interfere with the transferred RF wavelengths of interest during MRI operation.
Another aspect of the invention is to accomplish the aforesaid and at the same time satisfy space constraints.
In one aspect of the present invention, a thermal radiation shield is provided. The thermal radiation shield comprises a first coating layer and a second coating layer. A thermal shield layer is disposed between the first coating layer and the second coating layer. The thermal radiation shield has non-interfering electrical properties.
In accordance with the above and other objects, a method of applying a thermal radiation shield between a first surface and a second surface is provided. The method of applying the thermal radiation shield includes applying a first coating layer to the first surface. A second coating layer is then applied to the second surface. A thermal shield layer is then positioned between the first coating layer and the second coating layer.
Still another advantage of the present invention, is that it provides versatility allowing it to be applied to various MRI systems with varying space considerations. Another advantage of the present invention, is that higher magnetic gradient coil assembly temperatures of modern MRI systems are no longer a concern due to the infrared reflective and thermal properties of the present invention.
In addition, the present invention prevents degradation of RF electrical characteristics without generating spurious nMR signals. Therefore an infrared reflective thermal radiation shield with non-interfering electrical properties is possible due to the stated advantages.
The present invention itself, together with further objects and attendant advantages, is best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.